High pressure pumping apparatus with coupled volumes in a pump working chamber

ABSTRACT

A pumping apparatus ( 10 ), for delivering liquid at a high pressure at which compressibility of the liquid becomes noticeable, comprises a piston ( 20 ) adapted for reciprocation in a pump working chamber ( 30 ), wherein a movement of the piston ( 20 ) into a first direction ( 40 ) decreases a first volume (V 1 ) in the pump working chamber ( 30 ) and increases a second volume (V 2 ) in the pump working chamber ( 30 ), and a movement of the piston ( 20 ) into a second direction ( 50 ) opposite to the first direction ( 40 ) increases the first volume (V 1 ) and decreases the second volume (V 2 ). A coupling ( 70, 80, 90, 100 ) is provided for coupling the first volume (V 1 ) with the second volume (V 2 ) as long as a pressure (Psup) in the first volume (V 1 ) exceeds a pressure in the second volume (V 2 ). An outlet valve ( 120 ) is provided for coupling the second volume (V 2 ) with an outlet ( 110 ) of the pumping apparatus ( 10 ) as long as a pressure in the second volume (V 2 ) exceeds a pressure (Psys) at the outlet ( 110 ).

BACKGROUND ART

The present invention relates to a pumping apparatus for delivering liquid at a high pressure at which compressibility of the liquid becomes noticeable.

In high performance liquid chromatography (HPLC), a liquid has to be provided usually at very controlled flow rates (e.g. in the range of microliters to milliliters per minute) and at high pressure (typically 200-1000 bar and beyond up to even 2000 bar) at which compressibility of the liquid becomes noticeable. A general introduction into HPLC can be found e.g. under http://hplc.chem.shu.edu/HPLC/index.html. Some basic principles of reciprocating single piston pumps used in HPLC are described e.g. in http://hplc.chem.shu.edu/HPLC/index.html.

GB 1522552 discloses a pumping system for HPLC having a flow inducer to provide a high pressure metering are liquid.

EP 0309596 A1 discloses an HPLC pump system providing stroke volume variation in order to reduce pulsations.

U.S. Pat. No. 6,712,587 B2 discloses a hydraulic amplifier pump for use in HPLC.

DISCLOSURE

It is an object of the invention to provide an improved pumping apparatus for high pressure liquid delivery. The object is solved by the independent claim(s). Further embodiments are shown by the dependent claim(s).

Embodiments according to the present invention provide a pumping apparatus for delivering liquid at a high pressure at which compressibility of the liquid becomes noticeable. The pumping apparatus has a piston reciprocating in a pump working chamber having a first and a second volume. A movement of the piston into a first direction decreases the first volume and increases the second volume. Accordingly, a movement of the piston into a second direction opposite to the first direction increases the first volume and decreases the second volume. The first and second volumes are coupled to each other as long as a pressure in the first volume exceeds a pressure in the second volume. An outlet valve is provided for coupling the second volume with an outlet of the pumping apparatus as long as a pressure in the second volume exceeds a pressure at the outlet.

The coupling of the first and second volumes of the pump working chamber allows balancing forces onto the piston, so that a drive coupled to the piston for reciprocating the piston is exposed to lesser force requirements. This may allow using smaller drives which in turn may even provide an improved dynamic behavior and in general are usually less costly.

In one embodiment, the pumping apparatus has a given area proportion A between a first effective area of the piston facing the first volume and a second effective area of the piston facing the second volume. The first and second effective areas are opposing each other. With first effective area being greater than the second, a force required to move the piston is partly compensated, but still allowing to achieve a pressure increase in the second volume over the first volume. The force compensation becomes increased with the area proportion A getting closer to one, while greater area proportions A lead to less compensation and thus greater force requirements onto the drive of the piston. On the other hand, greater values of the area proportion A can lead to higher achievable pressure at the outlet of the pumping apparatus. Criteria for selecting the area proportion might be force requirements, dynamic, size, etc. of the piston drive. In some embodiments, area proportions (first effective area/second effective area) A of 2:1, 3:2, 4:3, etc. have been found useful for certain applications and balancing the contravening requirements of achievable outlet pressure and force requirements of the piston drive in certain applications.

In one embodiment, the first volume of the pump working chamber receives liquid at an inlet pressure, which can be ambient pressure or provided by an inlet pump. A control unit might be provided for controlling such inlet pressure to be in a given pressure proportion P to the pressure at the outlet of the pumping apparatus. The pressure proportion P (outlet pressure/inlet pressure) is preferably selected essentially in accordance with the area proportion A, to be A˜P. E. g. in case the pressure proportion is selected to be 2:1 (i.e. the first effective area is twice as large as the second effective area) the pumping apparatus can provide an outlet pressure of up to twice the inlet pressure. In case the pumping apparatus has to provide a certain outlet pressure (e.g. in order to drive a mobile phase through a stationary phase in a liquid chromatography application), the control unit might control the inlet pressure, whereas the outlet pressure then follows based on the given pressure proportion.

One or more pressure sensors for sensing values indicative of pressure might be provided at the inlet and/or outlet of the pumping apparatus, thus allowing to sense and control the pressures and/or the pressure proportion P.

The inlet pressure is preferably provided by an inlet pump coupled to at least one of the first and second volumes to provide liquid thereto at the inlet pressure. The inlet pump might be any kind of pump allowing to provide the liquid at the inlet pressure and might be embodied as a piston pump or a gear pump.

In one exemplary embodiment with A=P=2, the inlet pump is adapted to provide the liquid at 1/P (half in this example) of a required outlet pressure of the pumping apparatus, with the pumping apparatus providing a value of the area proportion A (2:1 in this example). If e.g. an outlet pressure of about 1200 bar is required with an inlet pump providing liquid to the inlet at about 600 bar, the pumping apparatus can thus deliver the liquid at the outlet at the about 1200 bar, but is only exerted to force requirements of 600 bar (i.e. the difference between the output and the input pressure: 1200 bar−600 bar=600 bar). In such embodiment, the inlet pump might be embodied mainly to provide the inlet pressure but with lesser accuracy requirements regarding liquid flow rate. The pumping apparatus, on the other hand, in this embodiment might be designed to provide flow rates at higher accuracy, so that in total a pump results allowing driving liquids with high flow rate accuracy and at high pressure.

In one embodiment, the piston is provided to have on one side the first effective area facing the first volume and on an opposing side the second effective area facing the second volume. The side of the piston facing the second volume is preferably coupled via a piston rod to a drive.

A return mechanism coupled to the piston and being adapted for counteracting against the movement of the piston might be provided to apply a force onto the piston in opposite direction as the drive, as well known in the art and disclosed e.g. in the aforementioned EP 0309596 A1, the teaching thereof shall be incorporated herein by reference.

Sealing might be provided for sealing the pump working chamber against the drive and/or to seal the first and second volumes against each other.

The drive might comprise at least one of a spindle drive mechanism, a linear motor, a stepper motor, a DC-Motor, a VR-Motor; a driving rod coupled to the piston.

The return mechanism might comprise at least one of a spring, a hydraulic cylinder, a drive mechanism, a deflection mechanism, a return rod coupled to the piston.

Valves applied might be one or more of a check valve, an active valve, a solenoid valve.

The inlet pressure might be in the range of 100 to 1000 bar, preferably between 300 and 700 bar, and more preferably about 600 bar. The achievable outlet pressure might be in the range of 500 to 2000 bar, preferably between 800 and 1500 bar, and more preferably about 1200 bar. A flow rate of the liquid at the outlet might be in the range of nanoliter per minute to milliliter per minute, and more preferably in the range of microliter per minute to milliliter per minute.

The coupling between the first and the second volumes can be provided by a conduit and preferably further comprises a coupling valve. In one embodiment, the first and second volumes are both coupled to the inlet pump, so that the coupling might also comprise the inlet pump.

Embodiments of the invention can be partly or entirely supported by one or more suitable software programs, which can be stored on or otherwise provided by any kind of data carrier, and which might be executed in or by any suitable data processing unit. Software programs or routines can be preferably applied to control the piston movement e.g. to minimize pump ripple and/or compensate physical effects influencing precision and accuracy.

BRIEF DESCRIPTION OF DRAWINGS

Other objects and many of the attendant advantages of embodiments of the present invention will be readily appreciated and become better understood by reference to the following more detailed description of embodiments in connection with the accompanied drawing(s). Features that are substantially or functionally equal or similar will be referred to by the same reference sign(s).

FIG. 1 shows an exemplary embodiment of a pumping apparatus 10 for delivering liquid at a high pressure at which compressibility of the liquid becomes noticeable.

FIG. 2 shows a more detailed embodiment of the pumping apparatus 10.

FIG. 3 shows an embodiment of a dual parallel pump 300 comprising to pumping apparatuses 10A and 10B, which can be embodied as shown in the FIGS. 1 and 2.

FIG. 4 shows another embodiment of a dual parallel pump in a principle drawing.

FIG. 5 shows a liquid separation system 500.

In FIG. 1, a piston 20 is reciprocating in a pump working chamber 30 having a first volume V1 and a second volume V2. A movement of the piston 20 into a first direction 40 decreases the first volume V1 and accordingly increases the second volume V2. Accordingly, a movement of the piston 20 in a second direction 50 (opposite to the first direction 40) increases the first volume V1 and decreases the second volume V2. The first and second volumes V1 and V2 are separated from each other in the pump working chamber 30, in the embodiment of FIG. 1 by a seal 60, which can be e.g. a polymeric piston seal as known in the art.

The first and the second volumes V1 and V2 are coupled to each other via a first conduit 70, a pressure supply 80, a second conduit 90, and a coupling valve 100. The pressure supply 80 is providing liquid at a pressure Psup. Due to the coupling of the first volume V1 and the pressure supply 80 via the first conduit 70, the volume V1 will also be under pressure Psup. Accordingly, due to the coupling of the second volume V2 with the pressure supply 80 via the second conduit 90 and the coupling valve 100, the second volume V2 will also be under pressure Psup. However, due to the unidirectional flow characteristics of the coupling valve 100, the second volume V2 will only be at pressure Psup as long as the pressure in the volume V2 does not exceed Psup.

Further coupled to the second volume V2 is an outlet 110, which might be coupled to a system at a pressure Psys. In the embodiment of FIG. 1, an outlet valve 120 is provided at the outlet 110, which also provides a unidirectional flow control, so that the outlet valve 120 is coupling the second volume V2 to the system Psys as long as the pressure in the second volume V2 exceeds the system pressure Psys.

Further in FIG. 1, a piston rod 130 is coupled to the piston 20 in order to move the piston 20. A drive 140 is coupling to the piston rod 130 in order to drive the piston 20. The drive 140 might comprise a return mechanism (not shown in FIG. 1) as known in the art. In the embodiment of FIG. 1, a drive seal 150 is provided for sealing the second volume V2 against the piston rod 130 and the drive 140. Details about the drive 140, the return mechanism, the rod 130 are disclosed e.g. in the aforementioned EP 0309596 A1 and shall be incorporated herein by reference.

In FIG. 1, the piston 20 has a first effective area A1 facing the first volume V1 and a second effective area A2 facing the second volume V2. In the embodiment of FIG. 1, the first effective area A1 is larger than the second effective area A2, and both effective areas A1 and A2 are at opposing sides of the piston 20. The ratio of the second effective area A1 to the first effective area A2 shall be denoted as A. In the example of FIG. 1, the ratio A is about 3:2.

The embodiment of FIG. 2 substantially corresponds to the principle drawing of FIG. 1. However, main difference is that the first volume V1 is directly coupled to the second volume V2 via the second conduit 90. Further, the coupling valve 100 is now located coupled directly to the outlet of the first volume V1. The second conduit 90, which might be embodied as a capillary, is coupled via a fitting 210 to the coupling valve 100 and via another fitting 220 to the second volume V2. Another fitting 230 is shown in FIG. 2 to couple another conduit 240, which might also be a capillary, to the outlet valve 120.

The first volume V1 receives the liquid via the first conduit 70 at the pressure Psup, and the second volume V2 outputs liquid at the outlet 110 at the pressure Psys.

Pressure sensors might be coupled to the inlet and/or the outlet of the pumping apparatus 10 in order to measure one or both of the pressures Psup and Psys, as shown e.g. in FIG. 3 below.

Operation of the examples in both FIG. 1 and FIG. 2 shall now be illustrated. Assuming that the pumping apparatus 10 is applied in an HPLC system (e.g. as illustrated later with respect to FIG. 5), so that the pumping apparatus 10 has to drive a mobile phase (as the liquid to be moved) through a chromatographic column coupled to the outlet 110. In most applications, the mobile phase has to be driven at a given and usually constant flow rate through the column, thus leading to a certain system pressure Psys (resulting from the hydraulic resistance of the system such as the column and capillaries).

In a first cycle, the piston 20 shall be at its left dead center, so that the first volume V1 being maximal and the second volume V2 being minimal. The first volume V1 is at the pressure Psup as provided from the pressure supply 80.

During the first cycle, i.e. when the piston 20 moves in the direction 40, the first volume V1 will be compressed and the liquid in volume V1 will be pressed out of the first volume V1. Due to the pressure increase in the first volume V1, the coupling valve 100 opens and supplies liquid into the second volume V2. Any liquid volume which cannot be filled into the second volume V2 (in case V2 is smaller than V1) will be provided (back) to the pressure supply 80. Alternatively, in case a second pumping apparatus is used e.g. in parallel (see below), liquid which cannot be filled into the second volume V2 can be provided to a first volume V1′ of such second pumping apparatus.

The ratio of the first effective area A1 to the second effective area A2 shall be A, and the input pressure Psup shall be selected (or is preferably controlled) to be the output pressure Psys divided by A. In this case, the movement of the piston into direction 40 will supply liquid from the first volume into the second volume. Due to the unidirectional valve 120 and as Psys should be larger than the pressure resulting in the second volume V2, there will be no supply of liquid into the system during the first cycle.

Once the piston 20 is at its right dead point and thereafter moves into the direction 50 during a second cycle, pressure in the second volume increases and the coupling valve 100 closes as soon as the pressure in V2 exceeds the pressure (Psup) in V1. At the same time liquid is sucked from the pressure supply 80 into the first volume V1 (at pressure Psup).

When the pressure in the second volume V2 reaches the system pressure Psys, the outlet valve 120 opens and the pumping apparatus 10 delivers liquid into the system during a third phase.

When the piston 20 reaches its left dead point, the process reverses and the afore-described sequence of phases one, two and three starts again.

During the third phase (i.e. supply phase), when the pumping apparatus 10 supplies liquid into the system, the liquid flow rate into the system is mainly determined by the second effective area V2 and the velocity of the movement of this piston 20.

Due to the effect of compressibility of the liquid, usually during the second phase, pulsation effects (i.e. pressure drops and over shooting) might occur, and adequate counter measures as known in the art can be provided. One way to encounter pulsation can be to expedite the second phase, i.e. to control the piston 20 to move faster during the beginning of the second phase.

As the piston 20 is facing both volumes V1 and V2 at its opposing ends, the piston 20 will experience forces from both volumes but in opposing directions, as indicated in FIG. 1. The pressure in the first volume V1 results in a first force F1 being proportional to the product of the pressure in the first volume V1 and the first effective area A1. Accordingly, a second force F2 is proportional to the pressure in the second volume V2 and the second effective area A2.

During the first phase when the piston 20 moves into the direction 40, the pressure in both volumes V1 and V2 is substantially the same as they are both coupled together. Thus, the resulting force onto the piston 20 is partly compensated. In case e.g. A=2 (A1=2*A2), only half (1-1/A) of the force is required over a pump system with only the first volume V1 (and no force compensation from V2).

In order to achieve a continuous supply of the liquid into the system usually two pumps are provided either in serial or parallel manner, as known in the art. The operation of both pumps is typically shifted by about 180 degrees, so that one pump is supplying into the system while the other is sucking liquid, and vice versa.

In the example of FIG. 3, first conduits 70A and 70B are coupled to the pressure supply 80, which might be a supply pump 310 and might have an outlet valve 320. An inlet pressure sensor 330 might be coupled to the common inlet of the pumping apparatuses 10A and 10B. The outlet 110A of the first pumping apparatus 10A and the outlet 110B of the second pumping apparatus 10B are coupled together to supply the system. A pressure sensor 340 might be coupled to the common outlets 110A and 110B. As illustrated above, liquid from the first volume V1 of the first pumping apparatus 10A which cannot be filled into the second volume V2 thereof can—in the embodiment of FIG. 3—be provided to a first volume V1′ of the second pumping apparatus 10B, and vice versa.

Similar to the example in FIG. 3 in a parallel manner, the two pumping apparatuses 10A and 10B can also be coupled in a serial manner (not shown in the figures), with the outlet 110A of the first pumping apparatus 10A being coupled to the inlet 70B of the second pumping apparatus 10B, and the outlet 110B of the second pumping apparatus 10B providing the outlet of the pump.

In the embodiment of FIG. 4, the two pumping apparatuses 10A and 10B share a common first volume V1. Both pistons 20A and 20B are moved either into direction 40 or the opposite direction 50. In this embodiment, the volume V1 remains substantially the same, and a compensation between both pumping apparatuses 10A and 10B is achieved. During the supplying phase of one of the two pumping apparatuses 10A and 10B, the supplying pump supplies virtually “through” V1 and the valve into V2 of the other pump, which at that phase is sucking liquid.

FIG. 5 shows a liquid separation system 500. A pump 400, which might be embodied as illustrated in FIG. 3 or 4, drives a mobile phase through a separating device 510 comprising a stationary phase. A sampling unit 520 is provided between the pump 400 and the separating device 510 in order to introduce a sample fluid to the mobile phase. The stationary phase of the separating device 510 is adapted for separating compounds of the sample liquid. A detector 530 is provided for detecting separated compounds of the sample fluid. A fractionating unit 540 can be provided for outputting separated compounds of sample fluid.

Further details of such liquid separation system 500 are disclosed with respect to the Agilent 1200 Series Rapid Resolution LC system or the Agilent 1100 HPLC series, as both provided by the applicant Agilent Technologies, under www.agilent.com which shall be in cooperated herein by reference. 

1. A pumping apparatus for delivering liquid at a high pressure at which compressibility of the liquid becomes noticeable, comprising a piston adapted for reciprocation in a pump working chamber, wherein a movement of the piston into a first direction decreases a first volumes in the pump working chamber and increases a second volume in the pump working chamber, and a movement of the piston into a second direction opposite to the first direction increases the first volume and decreases the second volume, a coupling for coupling the first volume with the second volume as long as a pressure in the first volume exceeds a pressure in the second volume, an outlet valve for coupling the second volume with an outlet of the pumping apparatus as long as a pressure in the second volume exceeds a pressure at the outlet, and a control unit adapted to control the inlet pressure to be in a given pressure proportion to the pressure at the outlet.
 2. The pumping apparatus of claim 1, wherein: a first effective area of the piston facing the first volume is in a given area proportion to a second effective area of the piston facing the second volume, wherein the first effective area is opposing the second effective area, and the first effective area is greater than the second effective area of the piston, so that a force required to move the piston into the first directions is partly compensated.
 3. The pumping apparatus of claim 1, wherein the first volume receives liquid at an inlet pressure, comprising at least one of: the pressure proportion of the inlet pressure to the outlet pressure is selected essentially in accordance to the area proportion of second are to the first effective area; an inlet coupled to the first volume for receiving liquid at the inlet pressure; a first pressure sensor adapted for sensing a value indicative of the inlet pressure; a second pressure sensor adapted for sensing a value indicative of the pressure at the outlet; an inlet pump coupled to at least one of the first volume and the second volume and is adapted to provide liquid thereto at the inlet pressure; the inlet pump comprises at least one of a piston pump, a gear pump, a hydraulic pump, a pneumatic pump.
 4. The pumping apparatus of claim 1, comprising at least one of: one side of the piston provides a first effective area facing the first volume, and an opposing side of the piston provides a second effective area facing the second volume; the side of the piston facing the second volume is coupled via a piston rod to a drive, a drive coupled to the piston adapted for reciprocating the piston; a return mechanism, coupled to the piston, being adapted for counteracting against the movement of the piston into a first direction and to apply a force onto the piston in order to move the piston into a second direction opposite to the first direction. a drive seal adapted for sealing the pump working chamber against the drive; a seal adapted for sealing the first volume against the second volume; the drive comprises at least one of a spindle drive mechanism, a linear motor, a stepper motor, a DC-Motor, a VR-Motor; a driving rod coupled to the piston; the return mechanism comprises at least one of a spring, a hydraulic cylinder, a drive mechanism, a deflection mechanism, a return rod coupled to the piston; the coupling comprises a coupling valve for coupling the first volume with the second volume as long as a pressure in the first volume exceeds a pressure in the second volume.
 5. The pumping apparatus of claim 1, comprising at least one of: the inlet pressure is in the range of 100 to 1000 bar, preferably between 300 and 700 bar, and more preferably about 600 bar; the achievable outlet pressure is in the range of 500 to 2000 bar, preferably between 800 and 1500 bar, and more preferably about 1200 bar; a flow rate of the liquid at the outlet is in the range of nanoliter per minute to milliliter per minute, and more preferably in the range of microliter per minute to milliliter per minute.
 6. The pumping apparatus of claim 1, further comprising a second pumping apparatus of claim 1, wherein the first and the second pumping apparatus are coupled in a parallel manner, with an inlet of the first pumping apparatus being coupled to an inlet of the second pumping apparatus, and an outlet of the first pumping apparatus being coupled to an outlet of the second pumping apparatus, thus providing an outlet of the pump.
 7. The pumping apparatus of claim 6, comprising at least one of: a liquid outlet of the first pumping apparatus is phase shifted, preferably essentially 180 degrees, with respect to a liquid outlet of the second pumping apparatus; the first and the second pumping apparatus have a common first volume in a common pump working chamber.
 8. A fluid separation system, comprising a separating device comprising a stationary phase for separating compounds of a sample fluid comprised in a mobile phase, and a pumping apparatus of claim 1, adapted for driving a mobile phase through the separating device.
 9. The separation system of claim 8, comprising at least one of: a sampling unit adapted for introducing the sample fluid to the mobile phase, a detector adapted for detecting separated compounds of the sample fluid, a fractionating unit adapted for outputting separated compounds of the sample fluid.
 10. A method of delivering liquid at a high pressure at which compressibility of the liquid becomes noticeable, comprising reciprocating a piston in a pump working chamber, wherein a movement of the piston into a first direction decreases a first volume in the pump working chamber and increases a second volume in the pump working chamber, and a movement of the piston into a second direction opposite to the first directions increases the first volume and decreases the second volume, coupling the first volume with the second volume as long as a pressure in the first volume exceeds a pressure in the second volume, coupling the second volume with an outlet of the pumping apparatus as long as a pressure in the second volume exceeds a pressure at the outlet, and controlling the inlet pressure to be in a given pressure proportion to the pressure at the outlet.
 11. A software product, embodied on a computer readable medium, for executing the control of the piston movement and for controlling the inlet pressure to be in a given pressure proportion to the pressure at the outlet in the method of claim 10, when run on a data processing system. 